Wireless networks, such as wireless sensor networks, serve a wide variety of applications, including monitoring, imaging, and tracking, for industrial and military applications. In wireless networks, it is often important for a network time to be defined, such that each node is able to assign network times to events in a manner that is consistent from node to node. One simple approach for providing a network time designates a node to act as a master node, to which the other nodes synchronize their respective local times (e.g., by receiving time stamped messages from the master node). However, this approach does not scale well to large networks, and it is difficult to apply it to certain cases of interest, such as ad hoc wireless networks. In an ad hoc network, nodes can join or leave the network depending on external events, so it is important to provide distributed synchronization. For example, if a master node were employed to provide synchronization in an ad hoc network, it would be highly disruptive if the master node were to leave the network.
To avoid this problem, various distributed synchronization methods have been proposed. In some approaches, local clocks at each node are synchronized. In other approaches, the local node clocks are not synchronized, but transformations of time stamps on received messages to local node time are performed. However, for either of these approaches, complications can be introduced by the need to properly account for message propagation delays between the nodes, especially since these delays can change as the physical configuration of the network changes. Another complicating factor in conventional synchronization approaches is the high precision and accuracy often required of time stamps (e.g., the IEEE 802.11 standard specifies a 64 bit timer having 1 μs resolution), which can place stringent demands on the performance of synchronization methods.
Accordingly, it would be an advance in the art to provide distributed synchronization for wireless networks that avoids these shortcomings.